1. Field of the Invention
The present invention relates to locks having a rotary blocking device that prevents a bolt from moving to an unlocked condition and a tamper resistant mechanism that prevents unauthorized access to a safe.
2. Description of the Related Art
Doors of safes, vaults, strong rooms, container and similar security closures (collectively called “safes” in this application) usually have at least one and preferably several safe bolts that reciprocate from a non-locking position to an extended locking position. In the locking position, the safe bolts extend from the safe door into the adjacent safe walls. When the safe has more than one bolt, bolt works connect the bolts. The bolt works include linkages that move the safe bolts simultaneously when a user turns a handle. A locking device cooperates with the bolt works to secure the safe bolts in their extended locking position.
Swing bolt or rotary bolt locking devices mount a bolt for pivoting between locked and unlocked positions. This application refers to the swing bolt within the locking device as the “bolt,” “swing bolt,” or “locking bolt.” The bolts that secure the safe door to the rest of the safe are called “safe bolts.” In the locked position, part of the locking bolt projects out of the housing and interferes with a portion of the mechanical bolt works, thereby preventing the bolt works from moving the safe bolts to the unlocked position. When the user enters the correct combination, the lock mechanism allows the locking bolt to pivot to the unlocked position within the housing, thus allowing the user to open the safe door.
Rectilinear bolt locking devices operate in a similar manner. In particular, rectilinear bolt locking devices mount a bolt within a housing for moving between locked and unlocked positions. Thus, instead of pivoting like rotary bolts, linear bolts slide into and out of the locking device housing. When the user enters the correct combination, the lock mechanism allows the locking bolt to slide into the housing. For purposes of explanation and example, the remainder of the background discussion will focus on rotary type locking devices.
In general, a handle on the outside of the safe connects to the bolt works. Rotating the handle initiates movement of the bolt works. If the user enters the correct combination which unlocks or releases the locking bolt, the bolt works can pivot the rotary bolt so that the rotary bolt does not project from the housing. This unlocked position permits the bolt works to continue moving the safe bolts to the unlocked condition, allowing the operator to open the safe. If, however, the rotary bolt is locked, the rotary bolt blocks movement of the bolt works, preventing the bolt works from withdrawing the safe bolts. U.S. Pat. Nos. 5,134,870 and 5,142,890 to Uyeda describe safes using rotary bolts.
The locking mechanism within the lock housing blocks the bolt from pivoting to the unlocked position. Uyeda utilizes a linear solenoid within the housing. Uyeda discloses a solenoid plunger that directly engages the locking bolt. Alternatively, the solenoid plunger engages a locking plate that projects against the bolt. When the plunger or plate engages the bolt, the bolt normally cannot rotate to an unlocked position.
An electronic combination entry system controls the solenoid. Typically, the user enters the combination through a digital input pad. U.S. Pat. No. 5,887,467 to Butterwerk, entitled “Pawl and Solenoid Locking Mechanism,” is an example of a lock that uses an electronic key pad on a rotary handle. Rotary input through a dial also can generate an output. Internal circuitry senses entry of the correct combination and sends an electrical signal to the solenoid. The signal causes the solenoid to withdraw a plunger, which, in turn, allows the locking plate to disengage the locking bolt. The user rotates a handle which in turn manipulates the bolt works. Part of the bolt works pushes on the locking bolt to rotate the bolt about a shaft to the unlocked position. The bolt works then withdraws the safe bolts.
Applying sufficient force, such as pounding, jostling, twisting, vibration, or other manipulation, on a locked handle of a safe with a swing bolt lock that is engaged with a plunger controlled by a linear solenoid can sometimes open the safe. This results because the solenoid must be relatively small to fit within the lock housing correspondingly, the plunger is also small and weak. Consequently, sufficient force applied to the handle breaks the plunger. Once the plunger breaks, or is vibrated out of the way, the locking plate moves freely, which allows the swing bolt to pivot open. The bolt works can then be manipulated to withdraw the safe bolts to open the safe.
Uyeda and others have proposed a solution to this problem by using a “safety key” design. The bore of the swing bolt, which rotates about a shaft or axle, is elongated. The elongated opening can move along the bore when one applies a force from the handle through the bolt works on the swing bolt. Thus, the swing bolt can move laterally. Lateral movement causes a notch on the periphery of the swing bolt to engage a safety key in the lock housing. This prevents further force being applied to the swing bolt from transferring to the solenoid plunger or locking plate.
Uyeda also discloses a leaf spring that biases the swing bolt and the bore to a normal position relative to the shaft within the bore. When an unauthorized user tries to force the handle without first entering the correct combination, the notched bolt pushes against and engages the safety key in the housing preventing entry.
The mechanism disclosed by Uyeda is complex and costly to build and assemble. Others have simplified the mechanism, but the structure that biases the swing bolt relative to the shaft or axle remains complex. For example, one conventional swing bolt has a bolt plate mounted in a groove in the swing bolt. The plate has an opening over part of the elongated opening in the swing bolt. A spring within the bolt biases the opening in the plate to one end of the elongated opening. When force is applied to the bolt to cause it to pivot about the solenoid locking plate, the bolt plate slides on the bolt against the spring until the opening in the bolt plate is at the other end of the elongated opening in the swing bolt. This shifts the swing bolt sufficiently to cause the notch of the periphery of the swing bolt to engage the key in the lock housing. The construction of the swing bolt with the sliding plate and internal spring is complex. Assembly is time consuming and costs are high. Furthermore, since the spring is within the bolt, a bearing is created between the shaft and the lock housing instead of between the swing bolt and the shaft, thereby reducing the potential life cycle of the lock.
An alternative design of a lock assembly is disclosed in U.S. Pat. No. 6,786,519 to Gartner. Gartner discloses a solenoid mounted within a housing and a plunger on the solenoid that engages a locking plate. When the lock is in the locked condition, the locking plate engages the locking bolt, preventing the swing bolt from pivoting. When a user enters the correct combination, the plunger disengages the locking plate so that the latter is free to slide out of its engagement with the locking bolt. If an unauthorized user applies sufficient force to the handle through the bolt works against the swing bolt, the intersection of the swing bolt and the locking plate becomes an axis of rotation. The swing bolt rotates slightly on that axis because the opening in the swing bolt through which the shaft extends is elongated. The elongation permits some lateral movement of the swing bolt relative to the shaft. As a result, a single notch on the swing bolt periphery engages a safety key on the housing preventing access.
Unfortunately, safety key mechanisms such as the one disclosed in '519 to Gartner provide insufficient protection against unauthorized access into the safe. Notably, a thin piece of shim stock such as steel may be positioned between the single notch and the safety key when the locking bolt is in the locked position. When the locking bolt is forcibly rotated, the thin shim acts as a “camming” surface, allowing the single notch to bypass the safety key element. As a result, force from the swing bolt may once again be applied against the solenoid plunger or locking plate, potentially resulting in damage to the plunger or solenoid within the lock housing.
Solutions such as those disclosed by Gartner and Uyeda that utilize linear solenoids to control movement of a plunger into and out of a locking bolt or a locking plate provide insufficient protection against “shock.” In the locked position, the plunger connected to the linear solenoid is extended such that it engages with, for example, a rotary locking bolt. In the unlocked position, the plunger retracts such that it no longer engages with the locking plate, thereby allowing the locking bolt to freely rotate. A problem arises when the linear solenoid, an electromagnetic device, receives a “shock.” Shock can be a result of physical tampering, applied force, vibration, etc. Typically, when a linear solenoid receives a shock, it causes an extended shaft (or in this case, the plunger) to retract in reaction to the shock. This poses a problem because the retraction of the plunger without entering the correct combination would effectively allow unauthorized access into the safe despite the addition of a notch and safety key feature.
Accordingly, there is a need for a lock having a blocking device that is simple to assemble, cost efficient, and that can reliably block access under force and shock. There is also a need for a tamper resistant mechanism that is more effective than the notch and safety key of conventional designs that prevents an unauthorized user from bypassing the safety key element and gaining access to the safe.